One established form of cancer treatment is irradiation by high-energy electromagnetic waves, typically X-rays. Solid tumors contain significant numbers of cells which are distal from the vasculature leading to oxygen deficiency or hypoxia. Hypoxia protects cells from radiotherapy. There is, therefore, a need for compounds which render the hypoxic cells more sensitive to killing by X-rays or the like. These compounds will be referred to herein as "radiosensitizers".
A variety of transition metal complexes have been shown to possess radiosensitizer activity. These include complexes of Ag, Cu, Zn, Hg, Pt, Co, Fe and Rh--1-13. The present invention is based on the finding that certain coordination compounds of cobalt and iron, namely Co(III) and Fe (III) coordination compounds, are potentially useful as radiosensitizers.